mmc: renesas_sdhi: Use devm_clk_get_optional() to obtain CD clock

Use the existing devm_clk_get_optional() helper to obtain the optional
Card Detect clock, instead of open-coding the same operation.
a side effect, real errors will now be handled correctly instead of
being ignored.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/540d803d31bf9aa1d0f78f431cae0ccd05387edc.1637069733.git.geert+renesas@glider.be

Author: geertu

drivers/mmc/host/renesas_sdhi_core.c

@@ -936,9 +936,9 @@ int renesas_sdhi_probe(struct platform_device *pdev,
 	 * to the card detect circuit. That leaves us with if separate clocks
 	 * are presented, we must treat them both as virtually 1 clock.
 	 */
-	priv->clk_cd = devm_clk_get(&pdev->dev, "cd");
+	priv->clk_cd = devm_clk_get_optional(&pdev->dev, "cd");
 	if (IS_ERR(priv->clk_cd))
-		priv->clk_cd = NULL;
+		return dev_err_probe(&pdev->dev, PTR_ERR(priv->clk_cd), "cannot get cd clock");
 
 	priv->pinctrl = devm_pinctrl_get(&pdev->dev);
 	if (!IS_ERR(priv->pinctrl)) {